Correlation retina in standard 0.6μm: application in positioning system

We have designed and fabricated a programmable retina that is capable of recognizing patterns stored in memory in real-time. Each of the pixels of the retina is composed of a photodiode and an electronic device used during the programming phase to digitize the image of the pattern to recognize into a binary image stored in latches. The array of pixels is thus partitioned into two complementary disjoint sub-sets with all the photodiodes of the same sub-set connected together in order to obtain the sum total of the currents. During the analysis phase, an optical correlation between the projected image and the reference binary image memorized in the circuit is done. The result is read-out as two voltages representing the following two currents: a “white” current proportional to the luminous flux falling on the photodiodes pertaining to the “white” part of the binary reference image and a “black” current corresponding to the black part. By comparing these two voltages to expected values, a shift of the pattern or a difference between the observed and programmed pattern can be detected. The retina has been fabricated in standard 0.6μm CMOS technology with three layers of metal from Austria Micro Systems. It consists of a 100×100 pixels image sensor. We present here an application of this sensor for industrial positioning system.